1. Field of the Invention
The present invention relates to a nitride-based nitride semiconductor device, more particularly which is improved in internal quantum efficiency, operating voltage and inverse voltage properties.
2. Description of the Related Art
In general, a nitride semiconductor layer is broadly applied to a green or blue light emitting diode (LED) used as a light source in full-color displays, image scanners, various signal systems and optical telecommunication devices, and a laser diode (LD).
Efficiency of the nitride semiconductor device is determined by internal quantum efficiency. i.e., recombination probability of electrons and holes in an active layer. In a major effort to boost the internal quantum efficiency, the active layer has been structurally improved and effective mass of carriers has been increased. Meanwhile, current crowding is mainly responsible for decline in efficiency of the nitride semiconductor device since carriers are not uniformly injected into the active layer.
Especially, current crowding is aggravated by inevitable arrangement of electrodes in the nitride semiconductor device. That is, when the nitride semiconductor device includes an insulating substrate such as a sapphire substrate, two electrodes are not disposed on opposed faces, but formed to face the same direction by mesa-etching an epitaxial layer. This is a planar nitride semiconductor light emitting device.
Such a planar nitride semiconductor device is disadvantaged in some aspects over a vertical light emitting device which has two electrodes formed on opposed faces of a light emitting structure. That is, in the planar nitride semiconductor device, current fails to travel uniformly across an overall light emitting area, thereby decreasing an effective light emitting area and also light emitting efficiency per light emitting area.
Therefore, in the art, to manufacture a high-efficiency nitride semiconductor device, there has arisen a need for a novel nitride semiconductor device which can spread current uniformly across the overall active layer to enhance light emitting efficiency.